This invention relates to the carbonylation of alkanols. More specifically, it pertains to a process for carbonylating alkanols in the vapor phase in the presence of a heterogeneous catalyst to produce dihydrocarbyl carbonates.
This invention also relates to a method for reactivating the heterogeneous catalyst used in the above process for carbonylating alkanols in the vapor phase to produce dihydrocarbyl carbonates.
The carbonates produced by this invention are well-known and are useful as synthetic lubricants, solvents and chemical intermediates in the preparation of polymeric derivatives such as clear plastics.
The traditional method for producing carbonates involves contacting phosgene with an appropriate alcohol. See Drake et al., J. Am. Chem. Soc., 52, 3720 (1960) and U.S. Pat. No. 2,379,250. This method results in the production of hydrogen chloride and thereby leads to the undesirable production of chlorine-containing by-products. In particular, the use of secondary alcohols leads to a significant formation of alkyl chlorides. Attempts to neutralize the hydrogen chloride have led to processing difficulties.
Other methods of producing carbonates generally involve the homogeneous liquid phase reaction of an alkanol, carbon monoxide and oxygen in the presence of a catalyst. For example, U.S. Pat. No. 4,360,477 describes a method for carbonylating alkanols with carbon monoxide and oxygen at elevated temperatures in the presence of copper salts. U.S. Pat. No. 4,370,275 discloses a process for preparing carbonates by reacting an alcohol, carbon monoxide and oxygen in the presence of a catalyst system containing copper, chemically bonded oxygen, chemically bonded halogen and at least one nitrogen base. The oxidative carbonylation process claimed in U.S. Pat. No. 4,426,331 involves the reaction of carbon monoxide, oxygen and an alcohol in the presence of a copper compound and a sulfone. U.S. Pat. No. 4,218,391 indicates that high acidity in carbonylation reactions involving metal salts leads to significant formation of by-products.
The above processes utilizing a homogeneous process require elaborate separation techniques to separate the organic base promoter in the azeotropic mixtures which can form between the dialkyl carbonate and the by-product water or unreacted alkanol. In addition, complex distillation steps are necessary to recover the catalysts for recycle to the processes. Due to the highly corrosive nature of most solutions containing copper halides and alkanols, expensive materials of construction are required for the reaction vessels and pipelines.
The above processes also do not provide for an efficient method of regenerating the catalysts used therein. Most catalysts can be regenerated by being subjected to acidic conditions. However, highly acidic conditions in the actual reaction mixture can lead to significant by-product formation. Therefore, over-acidification of the catalyst can lead to lower selectivities.
A process for the catalytic production of dihydrocarbyl carbonates is needed that would eliminate the above problems regarding separation and distillation and that would facilitate the regeneration of the catalyst utilized. An efficient method for regenerating the catalyst is also needed that would not interfere with the selectivity of the catalyst.